Background and aimsUnderstanding of the influences of soil moisture changes on plant phenological shifts on the Qinghai-Tibetan Plateau (QTP) is insufficient mainly because previous studies focused on the climatic factors. We explored the role of soil moisture in regulating plant autumn phenology on the QTP.MethodsBased on long-term ground observations of soil moisture, plant phenology, and meteorology, temporal and spatial changes in soil moisture and leaf senescence dates (LSD) were analyzed using ordinary least squares regression and a meta-analysis procedure. Influences of soil moisture changes on the LSD shifts were assessed through correlation analysis and support vector machine, and also compared with those of air temperature and precipitation.ResultsNonsignificant interannual changes in soil moisture were observed, and LSD significantly delayed at a rate of 2.7 days/decade. Spatial changes of LSD were more correlated with site elevation and air temperature, and soil moisture and precipitation showed insignificant negative impacts. However, correlations between annual LSD and average soil moisture were mainly positive. Soil moisture and precipitation showed greater importance in regulating the LSD of sedges and grasses, whereas temperature exerted a larger influence on the LSD of forbs. Precipitation showed higher importance in regulating the interannual shifts in LSD, while temperature played a more important role in determining the spatial variations.ConclusionSoil moisture had divergent influences on the temporal and spatial shifts in LSD of different plant functional groups on the QTP. Overall, soil moisture was outweighed by temperature and precipitation in regulating autumn phenological shifts. However, soil moisture may become increasingly important in the future and forbs are expected to be more competitive if the QTP becomes warmer and drier, which will bring challenges in grassland management and utilization on the QTP.

Tailings dust can negatively affect the surrounding environment and communities because the tailings are vulnerable to wind erosion. In this study, the effects of halides (sodium chloride [NaCl], calcium chloride [CaCl2], and magnesium chloride hexahydrate [MgCl26H2O]), and polymer materials (polyacrylamide [PAM], polyvinyl alcohol [PVA], and calcium lignosulfonate [LS]) were investigated for the stabilization of tailings for dust control. Erect milkvetch (Astragalus adsurgens), ryegrass (Lolium perenne L.), and Bermuda grass (Cynodon dactylon) were planted in the tailings and sprayed with chemical dust suppressants. The growth status of the plants and their effects on the mechanical properties of tailings were also studied. The results show that the weight loss of tailings was stabilized by halides and polymers, and decreased with increasing concentration and spraying amount of the solutions. The penetration resistance of tailings stabilized by halides and polymers increased with increasing concentration and spraying amount of the solutions. Among the halides and polymers tested, the use of CaCl2 and PAM resulted in the best control of tailings dust, respectively. CaCl2 solution reduces the adaptability of plants and therefore makes it difficult for grass seeds to germinate normally. PAM solutions are beneficial for the development of herbaceous plants. Among the three herbaceous species, ryegrass exhibited the best degree of development and was more suitable for growth in the tailings. The ryegrass plants planted in the tailings sprayed with PAM grew the best, and the root-soil complex that formed increased the shear strength of the tailings.

Context Plant roots can increase soil shear strength and reinforce soil. However, wetting and drying alternation (WD) could lead to soil structure destruction, soil erosion and slope instability.Aims This study tried to explore the effects of wetting and drying alternation on shear mechanical properties of loess reinforced with root system.Methods Direct shear testing was conducted on alfalfa (Medicago sativa L.) root system-loess composites with three soil bulk densities (1.2 gcm-3, 1.3 gcm-3 and 1.4 gcm-3) under 0, 1, 2 and 3 cycles of wetting and drying alternation (WD0, WD1, WD2 and WD3).Key results The morphological integrity of the root-loess composites was obviously better than the non-rooted loess after WD. Under the three soil bulk densities, negative power-law relationships were observed between the shear strength, cohesion and internal friction angle and the cycles of WD. WD deteriorated the soil shear strength. The most obvious decrease in soil shear strength occurred under WD1, which was 13.00-22.86% for the non-rooted loess and 17.33-25.09% for the root-loess composites. The cohesion was decreased more than the internal friction angle by WD.Conclusions The most obvious damage to the soil was under WD1. The roots inhibited the deterioration effect of WD on the shear property of loess, and the inhibition by the roots decreased with the cycles of WD.Implications The results could provide new insights into the mechanical relationship between plant roots and loess under WD, and provide a scientific basis for the ecological construction in the loess areas. Wetting and drying alternation (WD) on the mechanical properties of root-soil composites is not clear at present, or if roots can inhibit the deterioration of soil under WD. This paper investigated the effect of WD on the shear strength of root-loess composites. WD was found to deteriorate soil shear strength and cohesion, while roots inhibited the deterioration of WD on the shear property of loess. The results provide a scientific basis for ecological construction in loess areas.